Increasing acceptance of teleradiology, i.e. facsimile transmission of medical image information, and of digital archival storage of medical information as an alternative to film libraries has put great demand on means to first accurately convert information on x-ray film to a digital representation, and then to convert the digital information back to an image on x-ray film after storage or transmission. It is important not only to maintain accurately the information content between the original and the reproduced copy, but also to match exactly the visual appearance between the two. In actual use, laser film digitizers scan the x-ray film and convert image information into a digital representation of the actual density on the film. On the output side, laser film recorders are used to convert digital representations of density into image information on x-ray films.
Present laser film recorders use either red light from a He-Ne laser or infrared light from a diode laser for its scanning spot. Hence the films used to record the images on these laser film recorders have to be either red light sensitive or infrared light sensitive, depending upon the particular laser film recorder selected. The typical x-ray film used in radiology today all have blue or green sensitivity. Because of this, it is difficult to scan a conventional x-ray film and then reproduce it on a laser film recorder, matching its hue and color with the original film.
The differences in these two types of film, red sensitive and conventional black and clear mean that radiologists must learn to read and interpret images on the two films. This is not only burdensome, but the potential exists for misreadings of digital x-ray images. This is because the nature of reading radiographs is more like a skill that is developed with experience than something that can be taught. Therefore a radiologist experienced with conventional black and clear x-ray film may at first miss some of the subtle differences with red sensitive film.
Hospitals commonly have both conventional x-ray screen-film systems and digital radiography systems, thus familiarity with both systems is needed. It is important to note that there are other differences between conventional and digital radiography systems. For example, because the film used in the digital radiography system is sensitive to red light, it must be developed in total darkness. Standard black and clear x-ray film, on the other hand, is not sensitive to red light, and therefore a red light safety light may be used in the darkroom.
Laser scanning is also known in color film imaging. In U.S. Pat. No. 4,770,978 Matsuzaka discloses a method of producing a photographic image by scanning three separate laser beams, blue, green and red, onto a silver halide color photosensitive material having a blue-sensitive emulsion layer, a green-sensitive emulsion layer and a red-sensitive emulsion layer.
Therefore, in view of the above, it is an object of the present invention to devise a method for digital imaging which is more consistent with prior imaging methods and is more convenient than prior methods.